Diamagnetic to Cluster Glass Transition in the Mn-Substituted δ-Co2.5Zn17.5 Chiral Intermetallic Phase

Abstract

This study focuses on the binary δ-Co2.5Zn17.5 and pseudobinary δ-Co2.5–xMnxZn17.5 (x = 0–1.2) intermetallic phases, prepared via a high-temperature synthetic route. The crystal structure and atomic distribution of δ-Co2Mn0.5Zn17.5 were established using X-ray and neutron diffraction experiments. The pseudobinary δ-Co2Mn0.5Zn17.5 adopts a chiral crystal structure (P64), consistent with the binary δ-Co2.5Zn17.5. Theoretical calculations were employed to understand the site preferences of Co and Zn, as well as the overall phase stability of the binary compound. Interestingly, the substitution of Mn for Co occurs through Zn mediation (an indirect substitution). In the crystal structure, Mn occupies Zn sites at the 6c position; the displaced Zn then occupies the 3a site, ultimately maintaining the stoichiometry of Co2Mn0.5Zn17.5. The binary δ-Co2.5Zn17.5 exhibits diamagnetism, whereas Mn incorporation into the binary δ-Co2.5Zn17.5 induces cluster-glass magnetism in the pseudobinary δ-Co2Mn0.5Zn17.5, with a spin-freezing temperature of 10 K. While both compounds are structurally chiral, this chirality does not appear to influence their magnetic behavior. Instead, the cluster-glass state in the Mn-substituted phase is driven by the atomic randomness of the Mn atoms in the structural lattice. This out-of-equilibrium behavior below 10 K is further supported by the alternating-current (ac) magnetic susceptibility, thermoremanent magnetization, and the thermal memory effect.